Flexible electric heater and an apparatus and method for making the same



D. B. M cKENDRlCK I 2,423,196- FLEXIBLE ELECTRIC HEATER AND AN APPARATUS I Y AND METHOD FOR MAKI NG. THE SAME Filed Nov. 50,- 1943 I INVENTOR 7 D Mc/(swoawof D. B. M KENDRICK FLEXIBLE ELECTRIC HEATER AND AN APPARATUS AND METHOD FOR MAKING THE SAME Filed NOV. 50, 1943 July 1, 194 7.

2 Sheets-Sheet 2 INVENTOR DAV/0 5. MnJQwoR/cK 2'2 ATTORNEY sigh-n Patented July 1, 1947 seam i'wu UNITED STATES PATENT OFFICE FLEXIBLE ELECTRIC HEATER AND AN AP- PARATUS AND METHOD FOR MAKING THE SAME 8 Claims.

This invention relates to flexible electric heaters and to an apparatus and method for making the same. More particularly the invention pertains to heaters such as heating pads in which the heating coil is mounted directly on. a fabric sheet.

customarily, flexible electric heaters, such as electric heating pads, are provided with a fabric outer covering made, for example, from a woolen, cotton, silken or rayon felted, woven or knitted material which contacts the skin of the user. These coverings are widely employed, regardless of whether the heating element itself is enclosed in rubber or is mounted on an inexpensive fabric backing.

Such coverings have heretofore been essential when the coil was secured to a fabric backing since up to the present time the only commercially feasible method of attaching the coil to a fabric backing has been to stitch it to the backing along the entire convoluted length of the coil. Whether the coil was mounted on a single backing sheet or sandwiched between two such sheets, the sheets had to be covered to conceal this stitching.

It is an object of the present invention to eliminate the necessity for this additional covering by adhesively mounting the electric heating coil directly on the fabric sheet comprising the outer covering so that the coil attaching means does not how on the outer face of the fabric sheet and the heater need thus only comprise the outer covering, the heating coil and the usual accessories such as a thermostat and supply cord.

Another object of the invention is to provide an improved fabric heater and novel method of making the same in which a firm cementitious bond is rapidly effected between the heating coil and the fabric sheet whereby I am able to speed up the manufacture of such heaters and lower the production cost thereof.

An additional object of the invention is to provide a fabric heater in which the fabric sheet to which the heating coil is cementitiously attached comprises a hairy heavy cloth which accelerates adhesion of the coil, expedites formation of a strong cementitious bond, and presents a fiat outer surface despite the presence of the enclosed coil so that, if desired, the fabric sheet may itself constitute an external surface of the heater.

A further object of the invention is to provide an apparatus and method for making a fabric heater which will not distort, mutilate or pierce the backing sheet during mounting of the heating coil and which lend themselves to rapid manufacture of heaters at low cost and with com-paratively unskilled labor.

Other objects of the invention will in part be obvious and in part hereinafter pointed out.

The invention accordingly consists in the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter described, and of which the scope of application will be indicated in the claims.

In the accompanying drawings, in which is shown one of the various possible embodiments of this invention,

Fig. 1 is an exploded perspective view of a coil winding and transferring apparatus embodying my invention;

Fig. 2 is a perspective view of said apparatus with a heating coil wound thereon;

Fig. 3 is a perspective view of a fabric sheet prepared, in accordance with my invention, to receive a convoluted heating coil;

Fig. 4 is a erspective view of said apparatus and sheet during an early stage of th transfer of a convoluted heating coil to the sheet;

Fig. 5 is a similar view of said apparatus and sheet at a later stage of the transfer;

Fig. 6 is a perspective view of the sheet with the heating coil adhered thereto;

Fig. 7 is a perspective view of a completed heating pad made in accordance with and embodying my invention;

Fig. 8 is an enlarged sectional view taken substantially along the line 88 of Fig. 7, and

Fig. 9 is an enlarged sectional view through a portion of a fabric sheet which has been prepared in accordance with my invention for reception of a heating coil.

The coil winding and transferring apparatus with which I practice my invention basically comprises a means to wind a convoluted heating coil of predetermined size, boundary configuration and shape of convolutions, and associated means to transfer said coil in wound form from said winding means to a sheet prepared to adhesively receive the convoluted coil. Said apparatus preferably consists of a two-part template I0 including one part such as a board l2, hereinafter referred to as the base board, which has a plurality of projections l4 thereon, and another part such as a board I6, hereinafter referred to as the stripper board, which has a plurality of through openings such as apertures l8 arrayed in the same pattern as the projections I4 and of such size that the projections can freely pass therethrough whereby to permit the two parts to be arranged in proximate juxtaposition. The boards are made from a suitable form-maintaining material like plastic, metal or wood, plywood in particular being desirable because of its lightness, strength, low cost and easy machinability. The projections M are also made of a form-maintaining material like a blunt nail, a plastic pin, a steel peg, or a wooden dowel and are secured in conventional fashion to the base board. Said projections are so correlatively arranged as to provide a heating coil of a desired predetermined size, boundary configuration and shape of convolutions when resistance wire is wound therearound in any manner well known in the art, and, if desired, a plurality of such coils may be wound around the same or different projections in case, for example, the pad is to be made to operate at different temperatures by connecting different coils to a source of electric energy. It will be understood that the arrangement of the wooden dowels shown in the drawings is merely illustrative and that the pegs can be so mutually arranged as to obtain any desired number of convolutions of any desired size and boundary configuration.

Although the projections l4 and apertures l8 must be arranged in identically matching patterns, the base and stripper plywood boards l2, l6 need not be of the same size and, preferably, opposite portions, at least, of the stripper board project beyond the rim of the base board. In the illustrated example, I have effected this relationship by having the stripper board wider than the base board.

The tips of the projections M are coplanar and the projections are of such length that when the base and stripper boards are proximately juxtaposed the projections pass through the apertures I8 and their tips protrude from the stripper board a distance sufficient to permit heating wire to be Wound readily therearound.

For a reason which will shortly be apparent, if the material of which the stripper board is composed is such that the adhesive used in making the pad tends to stick to the board, I coat the upper surface l6a of said board facing away from the base board with a substance to which said adhesive does not stick. For example, if the stripper board is made of Wood, paraffin may be used for such coating.

The two-part template I is employed as follows to make a heating device embodying my invention: the stripper board I6 is so arranged that its apertures l8 overlie the tips of the projections l4 and said board is then abutted against the base board l2. At such time the tips of all of the projections l4 protrude above the surface of the stripper board remote from the base board and the assembled template has the appearance shown in Fig. 2. A resistance wire 20 is now wound about the protruding portions of the projections in any manner well known to the art and in accordance with a predetermined plan, for example, as illustrated in Fig. 2.

The resistance wire may be of any type conventionally used in the manufacture of electric heating devices of the character under consider ation. However, I prefer, for a purpose soon to be mentioned, to employ a resistance wire having a fibrous outer covering like an asbestos sheath 2| (Fi 8).

It may be mentioned that the resistance wire adjacent its ends may be criss-crossed intermediate each pair of projections in a linearly arranged set comprising several projections l4 whereby to enable the wire to better frictionally grip the projections and thus prevent it from accidentally slipping off the template. Also, while the boundary configuration of the coil is illustrated as being rectangular, it will be understood that boundary configurations of other outlines may be employed.

Before or after the resistance wire 20 is Wound on the assembled two-part template, I prepare a fabric sheet, such as a panel 22 (Fig. 3) to receive the convoluted heating coil. Said panel, in accordance with my invention, is composed of a flexible fabric material such, for instance, as would be normally used for the outer covering of a heating device. It may consist, by way of example, of a hairy, heavy cloth like cotton or woolen blanket material, illustrated in Fig. 3, which is a felted mass of cotton or woolen fibres, or, if the panel is not to form an outer surface of the device, of a cheaper hairy heavy cloth like jute.

Said panel, which is approximately the desired ultimate shape and plan contour of the finished heating device, is lightly sprayed with a heat-resisting flexible cement composed, e. g., of a volatile liquid vehicle having suspended therein dispersed particles of an adhesive substance like natural or synthetic rubber. I have found that both latex cement and the cement of a synthetic rubber like Neoprene give satisfactory results. The cement is applied with a conventional spray gun in such manner that it descends upon the panel 22 in a fine mist consisting of a great number of minute droplets. The spray will thus leave a fine coating of small globules 24 on the treated surface of the panel. These globules need not form a continuous layer but, as indicated in Fig. 9, may be discrete.

After the fabric panel 22 has been prepared in the foregoing manner, the two-part template is inverted to point the projections l4 downwardly. In this position the template is held over the treated surface of the panel and arranged relative thereto in a predetermined manner depending upon the position the convoluted wire 20 is to occupy on said panel. The template is then moved toward the panel until the tips of the projections are seated on the adhesively treated surface. It will be observed that at this time the stripper board l6, which is now below the base board l2, extends laterally beyond said base board so that it can be manipulated easily. These extending portions of the stripper board are grasped by the operator and urged towards the panel 22 causing the convoluted heating wire ill to slip along the projections l4 towards said fabric panel. By the time the stripper board contacts or is close to the fabric panel, it will have almost fully pushed the convoluted wire coil off the projections l4 and transferred it to the adhesively treatedfabric surface. This position of the template and panel is illustrated in Fig. 4.

The base board can now be removed to completely strip the wire from the projections and leave the stripper board and convoluted coil on the fabric panel, as shown in Fig. 5. Next said stripper board is pressed lightly, by hand, for a few moments against the fabric panel to better force the coil into contact with said panel and then said board also is removed. When the stripper board is lifted free, the coil will be firmly adhesively secured to the fabric panel substantially as shown in Fig. 6, a bond having been quickly effected between said panel and coil.

However, I may leave the coil and panel stand until a suitable number of panels have had coils attached thereto during which time the adhesive spray will dry.

It will be noted that, due to the fact that the surface of the stripper board which contacts the adhesively treated surface of the fabric panel is treated with wax, the stripper board can be removed easily. The wound heating wire 20, however, will adhere to the fabric panel, particularly where it includes a covering of fibrous material like the asbestos sheath 2|.

Particular attention is directed to the speed with which a firm cementitious bond is created between the panel and resistance wire. This is believed to be due to two factors, of which the most important is thought to be the application of the cement to the panel in discrete globules. I have found that otherwise, if a continuous layer of cement is applied to the panel, considerably more time is required to effect a good bond between the panel and wire and this necessitates leaving the stripper on longer and pressing it against the panel and wire over a greater period of time. The second influencing factor is believed to be the hairy surface and, possibly, the coarse texture of the fabric which permits a ready and thorough surface penetration of the fabric by the cement around the area of bonding between the fabric and wire.

Next the convoluted and attached heating wire is equipped with conventional accessories such, for example, as a thermostat 26 (Fig. 6) and a supply cord 28 which are secured to said coil in any manner known to the art.

If desired, the ends of the wire when wound about the projections I4 may be coated with a substance such as wax to prevent the same from adhering to the cementitiously treated fabric panel, so that at the time the thermostat and supply cord are fitted to the coil the two ends of the heating wire will be free of said panel. The portion of the asbestos sheath so treated can be stripped from the heating wire during attachment of the thermostat and supply cord. However, if such procedure is not practiced, I can alternatively, lift up the ends of the convoluted wire to which the thermostat and supply cord are to be attached, either before the adhesive has fully set, or even after it has set by rupturing the asbestos sheath where the accessories are to be secured.

After the thermostat and supply cord have been attached, I may temporarily hold the supply cord in place with a small piece of adhesive tape 30. Before being applied, the supply cord may be coated with rubber cement, the coating on the supply cord, of course, stopping short of its point of exit from the heating device.

Next I prepare another fabric panel 32, similar to the panel 22, depositing thereon discrete cementitious globules like the globules 24. Said second panel, as soon as the adhesive has been deposited thereon, has its treated surfac placed on the wire carrying surface of the first panel and a light rubbing manual pressure is applied over the panels to firmly cement the two sprayed surfaces of the fabric together. Again a firm adhesive bond is very rapidly formed between the two panels and between the resistance wire and second panel due to the presence of a hairy surface on the fabric and the sparing use of cement which causes the adhesiv material to be deposited as small discrete globules on the second panel.

Thus good adhesion is secured within a few seconds and the two attached panels can be stacked, together with other cemented panels of the same type, and allowed to dry before the next operation. Once th cement is dried, it is impossible to tear the two pieces of fabric apart without rupturing the fabric itself, and the wire is so firmly held in place that it will not shift from its predetermined position.

After the adhesive is thoroughly set, the cemented pair of fabric panels are provided with a finished edge by securing a binding tape 34 around the rim of said panels with a line of stitching 36. A few additional lines of stitchin 38 are sewed through th blanket material over the supply cord 30 a short distance, say onehalf an inch, from where the said cord leaves the pad in order to provide additional strain relief.

The heating devic 40 is now complete and can, if desired, be provided with a removable waterproof envelope such as is stipulated by the Underwriters Testing Laboratories for protection against perspiration and water. It will be appreciated that the pad thus produced comprises a minimum number of parts due to the fact that the outer fabric covering itself carries the heating coil without having been inpregnated in a costly manner with a fluid rubber composition to embed the coil in solid rubber or in a rubber film of appreciable thickness.

It will thus be seen that I have provided a heating device, and method and apparatus for making the same, in which the several objects of this invention ar achieved, and which is well adapted to meet all conditions of practical use.

As various possible embodiments might be made of the abov invention, and as various changes might be made in the embodiment above set forth, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, I claim as new and desire to secure by Letters Patent:

1. In a method of manufacturing a heating device having a convoluted wire heating coil of predetermined size, boundary configuration and shape of convolutions by means of a template comprising two abutting parts whereof one part has a plurality of projections having coplanar tips arrayed to conform to said convoluted coil, and whereof the other part has a plurality of through openings arranged in the same pattern as the said projections and freely receiving the same and allowing the tips thereof to protrude: the steps comprising winding resistance wire around the protruding tips of said projections and then stripping said wound wire from said projections by moving said parts away from each other and transferring said wound wire to an adhesive surface as it is stripped from the projections.

2. In a method of manufacturing a heating device having a wire heating coil of predetermined size, boundary configuration and shape of convolutions with the use of a two-part template, one of whose parts has a plurality of projections thereon conforming to the predetermined size, boundary configuration and shape of convolutions of said coil, the tips of the projections being coplanar, and the other of the parts having a plurality of through openings arrayed in the same pattern as the projections and large enough to permit the projections to pass freely therethrough, said projections being of such length in relationship to said openings that the tips of the projections protrude therethrough when said parts are assembled by abutment: the steps comprising winding resistance wire around the protruding tips of said projections in said assembled template, preparing a hairy fabric panel to receive said wound wire by adhesively treating a surface of said panel, then stripping said wound wire from said projections by moving said parts away from each other, and transferring said wound wire to the adhesively treated surface of said panel as it is stripped from the projections.

3. A method as set forth in claim 2 wherein the coplanar tips of the projections are seated on the adhesive treated surface of the panel before the wound wire is stripped therefrom.

4. A method as set forth in claim 2 wherein the tips of the projections are seated on the adhesive treated surface of the panel before the wound wire is stripped therefrom and wherein the part with projections is removed and the part with openings, which is left on, pressed against the stripped wound wire and panel before it too is removed.

5. A method as set forth in claim 2 wherein after the wound wire is adhesively attached to the panel a second hairy fabric panel has a surface thereof adhesively treated and said second panel is subsequently placed with its adhesively treated surface in contact with the wire carrying surfaces of the first mentioned panel.

6. A method as set forth in claim 2 wherein the panel is adhesively treated by disposing discrete globules of an adhesive over a hairy surface thereof.

7. A method as set forth in claim 2 wherein after the wound wire is adhesively attached to the panel a second hairy fabric panel has a surface thereof adhesively treated and said second panel is subsequently placed with its adhesively treated surface in contact with the wire carrying surfaces of the first mentioned panel, and wherein both panels are adhesively treated by disposing discrete globules of an adhesive over hairy surfaces thereof,

8. In the manufacture of electric heating de vices the step comprising winding a heating wire on a plurality of parallel bars having a predetermined correlation and then simultaneously stripping said wire from all said bars and at the same time tfansferring the wound wire to a hairy fabric panel adhesively prepared to receive I said wound wire.

DAVID B. MACKENDRICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,804,916 Cotte May 12, 1931 1,384,467 Homan July 12, 1921 2,022,519 Payne Nov. 26, 1935 1,885,690 Doyle Nov. 1, 1932 2,052,644 Murphy Sept. 1, 1936 2,334,671 Gibbons Nov. 16, 1943 2,334,668 Conner Nov. 16, 1943 1,905,690 Doyle Apr. 25, 1933 2,349,956 Gliss et a1. May 30, 1944 2,238,342 Riehl Apr. 15, 1941 FOREIGN PATENTS Number Country Date 65,826 Australia July 25, 1914 

